Náměty na pokusy a pozorování vodních živočichů ve školním akváriu vi – chov a odchov potápníků

with strong, paddle-like hind legs that propel them easily in water. A large bubble of air under the beetle wing covers (elytra)
allows them to suck in a bubble of air from the water surface, as well as breathe underwater for long periods of time without
coming to the surface. A total of 127 species of the family Dytiscidae are currently reported as being in the Czech Republic.
A suitable species for breeding in an aquarium is the Great Diving Beetle (Dytiscus marginalis) (see Fig.11). A voracious
predator, this beetle hunts a wide variety of prey including small fish. Interestingly, it is very easy to distinguish between
the sexes of Dytiscus marginalis as females have parallel grooves running down their elytra (back or top surface), see Fig.
11, whereas males have smooth elytra. But this characteristic is not 100% reliable, because females sometimes also have
smooth elytra. A reliable distinction is made by the conspicuous sucking discs at the end of the first pair of legs (see Fig. 4).
The aquarium equipment should be as follows: water to a depth of 20 cm or greater, ideally closer to room temperature.
Underwater surfaces for the beetles to rest on, such as plants, rocks, or twigs. A cover on the top is very important (the beetles
can fly). A piece of floating wood will do, or a rock that reaches above the water. No water filtration or aeration equipment is necessary. Both adults and larvae (see Fig. 7) are voracious predators feeding on anything in their reach, including larval
fish. The healthiest and most entertaining foods for diving beetles are fresh invertebrates, meal worms, earth worms; small
pieces of lean meat can also be used. Diving beetles can attack fish (sick and injured ones especially) even if they are larger,
and eat them. Diving beetles also have a fascinating defense mechanism: they secrete toxic substances that can make vertebrates,
such as fish, sick if both are kept in a shared environment. Eggs are laid in or on vegetation beneath the water surface,
or on other objects below or just above the surface. The larvae develop over a period of a few to several weeks, then leave the
aquatic habitat to pupate in cells (see Fig. 8) that they construct in the soil of protected areas nearby (an aqua-terrarium
must be provided for the successful pupation of larvae). The pupal stage (see Fig. 9) lasts 5–14 days, after which the adult
emerges and usually re-enters the aquatic habitat. Some experiments on, and observations of, larvae and adult predaceous
diving beetles in an aquarium, inspired by cited literature sources, are presented in this contribution.